In the prior art, there are two kinds of golf balls. The one is a solid golf ball, such as a two-piece solid golf ball, which is composed of a core of an integrally molded rubber member and a thermoplastic resin (e.g. ionomer resin, etc.) covered on the core. The other is a thread wound golf ball and is obtained by winding thread rubber on a solid or liquid center and covering it with a cover of an ionomer resin, balata, etc. having a thickness of 1 to 2 mm. The two-piece solid golf ball is used by many golfers, particularly amateur golfers, because of good durability, longer flight distance attained by high ball velocity at the time of hitting and excellent flight performance in comparison with the thread wound golf ball. On the other hand, the two-piece solid golf ball has a problem wherein the shot feel at the time of hitting is hard.
In order to improve the drawback of the two-piece solid golf ball, softening the cover or the core has been suggested, but the softening adversely lowers the rigidity of the golf ball and reduces the impact force of the golf ball at the time of hitting, which results in a reduction in flight distance.
In addition, in order to improve this drawback, it has been tried to make the core and the cover of multiple layers. However, a two piece solid golf ball having satisfactory performance has not yet been obtained.
In order to improve the shot feel of a solid golf ball, a hollow portion golf ball having a hollow core at its center has been proposed in Japanese Utility Model Publication No. 3(1992)-63354. By forming a hollow portion in the center of the golf ball, the weight is disposed to the outside of the golf ball to increase moment of inertia, thereby making it possible to increase the flight distance. Since the hollow portion is present at its center, the impact force at the time of hitting can also be reduced.
Although it is actually possible to increase the moment of inertia by forming a hollow portion inside of the golf ball, the golf ball weight is undesirably reduced. To compensate for the ball weight, the rubber composition for the golf ball is made heavier or with a higher specific gravity by adding thereto a larger amount of a filler. The formulation of a filler in a larger amount adversely decreases the rubber content in the rubber composition to result in the degradation of the rebound characteristics. With respect to the impact force upon hitting, providing a hollow portion inside of the golf ball increases the deformation of the golf ball upon hitting and reduces the impact force, thus reducing the shot feel upon hitting. However, the larger the deformation of the golf ball, the larger the energy loss which often degrades the rebound characteristics.